1. Field of the Invention
The present invention generally relates to a method of and an apparatus for detecting an angular velocity on the basis of an output voltage of an angular velocity sensor such as a gyro or the like and to a method of and an apparatus for detecting an angle on the basis of the output voltage of the angular velocity sensor such as a gyro or the like. The present invention also relates to a navigation system including the above-mentioned apparatus for detecting an angle, a program storage device and a computer data signal embodiment in a carrier wave, which allow a computer to function as the apparatus for detecting an angle or angular velocity.
2. Description of the Related Art
Conventionally, there is an angular velocity sensor such as a gyro or the like among instruments mounted on various types of movable things, and it is mounted, for example, on a movable body such as a vehicle, an airplane, a rocket, a ship or the like for detecting an angle or an angular velocity, or on a robot for controlling its attitude, or on a video camera for correcting movement of the hand. There is also an apparatus for detecting an angle, which displays or records after calculation of an angle, and further an apparatus for detecting an angular velocity, which displays or records after calculation of an angular velocity, on the basis of an output voltage of the angular velocity sensor in this kind.
For example, an on-vehicle navigation system is equipped with the angular velocity sensor such as a vibration gyro or the like and it calculates a drive azimuth on the basis of its output voltage and displays the calculated drive azimuth on a display map in a predetermined format. Alternatively, it is constructed to calculate a current position by a dead reckoning positioning measurement by using a drive distance obtained from a drive distance sensor or the like in conjunction with the calculated drive azimuth, and to display the calculated current position in a predetermined format on the display map.
The angular velocity sensor in this kind is constructed to set a bias voltage, which is an output voltage outputted when the angular velocity is zero, as a standard voltage and to calculate an angle on the basis of this standard voltage and an output voltage of the angular velocity sensor at an arbitrary time. Alternatively, it is constructed to calculate the angular velocity by how high the output voltage of the angular velocity sensor at the arbitrary time is, including its polarity, with the standard voltage as a standard.
Especially here, as for the angular velocity sensor such as a vibration gyro or the like, its bias voltage changes stepwise by a temperature drift and a start drift. Therefore, if the bias voltage on startup is fixed as the standard voltage, the detected drive azimuth may disadvantageously change gradually in spite of direct advance of a vehicle, for example. To avoid this, Japanese Patent Application Laying Open NO. Hei 5-52578 discloses a method of decreasing effects of the temperature drift or the like by updating the bias voltage, which is the output voltage of the angular velocity sensor, as a new standard voltage when it is detected that a vehicle is stopping on the basis of a vehicle speed obtained from an apparatus for detecting a vehicle speed.
According to the above-mentioned Japanese Patent Application Laying Open NO. Hei 5-52578, the effects of the temperature drift of the bias voltage or the like can be decreased when updating the standard voltage or just after that. However, because the standard voltage is not updated but constant, considering about a period until the standard voltage is updated next time, the effects of a change by the temperature drift of the bias voltage or the like reveal themselves remarkably with time passing by. Moreover, the standard voltage is not updated as long as such a drive condition that the standard voltage can be updated is not obtained. Therefore, as such a period that the standard voltage is not updated becomes longer, the errors of an angle caused by the change by the temperature drift of the bias voltage or the like increase. Consequently, the drive azimuth of a vehicle displayed on a display map departs widely from a road direction depending on the elapsed time from when the standard voltage, which is generally unknown to a driver, is updated, for example, which is a big problem in practice.
Furthermore, a similar problem applies to a general apparatus for detecting an angular velocity equipped with an angular velocity sensor, and the angular velocity to be detected may have errors depending on the elapsed time after updating the standard voltage by the effects of the temperature drift of the bias voltage described above or the like as well.
It is therefore an object of the present invention to provide a method of and an apparatus for detecting an angular velocity as well as a method of and an apparatus for detecting an angle, which can decrease the errors caused by the change by the start drift, the temperature drift or the like of the bias voltage of the angular velocity sensor such as a gyro, and further a navigation system equipped with the apparatus for detecting an angle, a program storage device and a computer data signal embodiment in a carrier wave, which allow a computer to function as the apparatus for detecting an angle or angular velocity.
The above object of the present invention can be achieved by a method of detecting an angular velocity provided with processes of: setting a bias voltage, as a standard voltage, which is an output voltage outputted from an angular velocity sensor in response to an angular velocity when a predetermined condition is satisfied as well as updating the standard voltage every time the predetermined condition is satisfied; calculating the angular velocity on the basis of the output voltage with using the set or updated standard voltage as a standard; storing time data, which indicate a time of setting or updating the standard voltage, in correspondence with standard voltage data, which indicate a value of the set or updated standard voltage; estimating a value of the bias voltage of the angular velocity sensor at each time between times of setting or updating the standard voltage, as a function of time, on the basis of a plurality of the stored standard voltage data and a plurality of the stored time data; and correcting the angular velocity calculated by the calculating process on the basis of a difference between a value of the standard voltage used in the calculating process and the estimated value of the bias voltage.
According to the method of detecting an angular velocity of the present invention, the bias voltage, which is the output voltage outputted from the angular velocity sensor such as a gyro, is firstly set as the standard voltage when such a predetermined condition that a movable body in various types such as an airplane, a rocket, a ship, a vehicle or the like, or a movable thing such as a robot, a video camera or the like, on which the angular velocity sensor is mounted, is stopping, is straightly advancing or the like is satisfied as an initial condition, for example. Then, after the method of detecting an angular velocity is started, every time this predetermined condition is satisfied, the standard voltage is updated by the setting process. Then, the angular velocity is calculated by the calculating process on the basis of the output voltage with using the set or updated standard voltage as a standard. Normally, the angular velocity is calculated in response to how high the output voltage is, including the positive and negative polarity, with respect to the standard voltage. On the other hand, the time data, which indicate a time of setting or updating the standard voltage, is stored into a memory or the like by the storing process, in correspondence to the standard voltage data, which indicate a value of the set or updated standard voltage, every time the standard voltage is set or updated. Then, the value of the bias voltage of the angular velocity sensor at each time between times of setting or updating the standard voltage is estimated by the estimating process as the function of time. This estimation is performed, under a condition that at least two time data and two standard voltage data corresponding to the time data are stored, on the basis of these standard voltage data and time data. Then, the angular velocity calculated by the calculating process in the past is corrected by the correcting process, on the basis of the difference between the value of the standard voltage used in the calculating process and the above-mentioned estimated value of the bias voltage.
Therefore, within a period while the bias voltage can not be measured, the calculated angular velocity more or less includes errors caused by a change by the start drift, the temperature drift of the bias voltage or the like. However, when the standard voltage is updated next time, i.e., when the bias voltage can be measured next time, the errors caused by the change of the bias voltage can be corrected backward into the past.
Incidentally, the bias voltage value not only in the past but also in the future may be estimated by the estimating process, from the latest time of updating and may be used as the standard voltage in calculating the angular velocity before the correction.
In one aspect of the method of detecting an angular velocity, the method is further provided with a process of judging whether or not the predetermined condition is satisfied, wherein the setting process sets or updates the standard voltage depending on a judgment result in the judging process.
According to this aspect, it is judged by the judging process whether or not the predetermined condition is satisfied such as whether or not the velocity of the movable thing is less than a certain value, whether or not a velocity change is within a constant range, or the like. Then, the standard voltage is set or updated by the setting process, depending on this judgment result in the judging process. Therefore, because the standard voltage can be certainly set or updated when the bias voltage can be newly measured, it is possible to set the standard voltage with a high accuracy.
In another aspect of the method of detecting an angular velocity, the estimating process uses an n function (n-dimensional function) (n is a natural number), which approximates a change of the bias voltage value with respect to time, as the function.
According to this aspect, the estimating process uses an n function or n-dimensional function such as a linear function, i.e., a straight line, a quadratic function, i.e., a parabola, a cubic function or the like as the function. For example, an n function in this kind is obtained by solving simultaneous equations made by n standard voltages in the past and the corresponding times. Moreover, it is possible to estimate a change of the bias voltage value from more standard voltage values, by using the least square method for n+2 or more standard voltage values in the past.
The above object of the present invention can be achieved by a method of detecting an angle provided with processes of: setting a bias voltage, as a standard voltage, which is an output voltage outputted from an angular velocity sensor mounted on a movable thing in response to an angular velocity when a predetermined condition is satisfied, as well as updating the standard voltage every time the predetermined condition is satisfied; calculating the angle of the movable thing on the basis of a difference between the output voltage and the set or updated standard voltage; storing time data, which indicate a time of setting or updating the standard voltage, in correspondence with standard voltage data, which indicate a value of the set or updated standard voltage; estimating a value of the bias voltage of the angular velocity sensor at each time between times of setting or updating the standard voltage, as a function of time, on the basis of a plurality of the stored standard voltage data and a plurality of the stored time data; and correcting the angle calculated by the calculating process on the basis of a difference between a value of the standard voltage used in the calculating process and the estimated value of the bias voltage.
According to the method of detecting an angle of the present invention, the bias voltage, which is the output voltage outputted from the angular velocity sensor such as a gyro, is firstly set as the standard voltage when such a predetermined condition that a movable thing is stopping, is advancing direct, or the like is satisfied as an initial condition, for example. Then, after the method of detecting an angle is started, every time when the predetermined condition is satisfied, the standard voltage is updated by the setting process. Then, the angle of the movable thing (e.g., the travel azimuth or direction of a vehicle) is calculated by the calculating process, on the basis of the difference between the output voltage and the set or updated standard voltage. Normally, a turning angle of the movable thing is calculated by integrating the difference between the output voltage and the standard voltage, and the angle of the movable thing is calculated by adding this turning angle onto the angle before its turning. On the other hand, the time data, which indicate a time of setting or updating the standard voltage, is stored into a memory or the like by the storing process, in correspondence with the standard voltage data, which indicate a value of the set or updated standard voltage, every time when the standard voltage is set or updated. Then, the value of the bias voltage of the angular velocity sensor at each time between times of setting or updating the standard voltage is estimated by the estimating process, as the function of time. Here, this estimation is performed, under a condition that at least two time data and two standard voltage data corresponding to the time data are stored, on the basis of these standard voltage data and time data. Then, the angle calculated by the calculating process in the past is corrected by the correcting process, on the basis of the difference between the value of the standard voltage used in the calculating process and the above-mentioned estimated value of the bias voltage.
Therefore, within a period while the bias voltage can not be measured, the calculated angle includes errors caused by a change by the start drift, the temperature drift of the bias voltage or the like. However, when the standard voltage is updated next time, i.e., when the bias voltage can be measured next time, the errors caused by the change of the bias voltage can be corrected backward into the past.
Incidentally, the bias voltage value not only in the past but also in the future may be estimated by the estimating process, from the latest time of updating and may be used as the standard voltage in calculating the angle before the correction.
In one aspect of the method of detecting an angle, the method is further provided with a process of judging whether or not the predetermined condition is satisfied, wherein the setting process sets or updates the standard voltage depending on a judgment result in the judging process.
According to this aspect, it is judged by the judging process whether or not the predetermined condition is satisfied such as whether or not the velocity of the movable thing is less than a certain value, whether or not a velocity change is within a constant range, or the like. Then, the standard voltage is set or updated by the setting process, depending on this judgment result in the judging process. Therefore, because the standard voltage can be certainly set or updated when the bias voltage can be newly measured, it is possible to set the standard voltage with a high accuracy.
In another aspect of the method of detecting an angle, the estimating process uses an n function (n is a natural number), which approximates a change of the bias voltage value with respect to time, as the function.
According to this aspect, the estimating process uses an n function or n-dimensional function. For example, an n function in this kind is obtained by solving simultaneous equations made by n standard voltages in the past and the corresponding times. Moreover, it is possible to estimate a change of the bias voltage value from more standard voltage values by using the least square method.
In another aspect of the method of detecting an angle, the calculating process converts a value, which is obtained by integrating on a time axis a difference between the output voltage and the set or updated standard voltage to a turning angle of the movable thing and the correcting process corrects the angle by correcting the turning angle in response to a value, which is obtained by integrating on a time axis a difference between the value of the standard voltage value used in the calculating process and the estimated value of the bias voltage.
According to this aspect, it is possible to calculate the turning angle of the movable thing relatively easily by the difference between the output voltage of the angular velocity sensor and the standard voltage by use of an integrating circuit. Further, it is possible to calculate a correction amount to the turning angle relatively easily by the difference between the standard voltage value used in the calculating process and the estimated value of the bias voltage by use of the integrating circuit. Therefore, it is possible to correct the angle on the basis of the corrected turning angle.
The above object of the present invention can be achieved by an apparatus for detecting an angular velocity provided with: a setting device for setting a bias voltage, as a standard voltage, which is an output voltage outputted from an angular velocity sensor in response to an angular velocity when a predetermined condition is satisfied as well as updating the standard voltage every time the predetermined condition is satisfied; a calculating device for calculating the angular velocity on the basis of the output voltage with using the set or updated standard voltage as a standard; a storing device for storing time data, which indicate a time of setting or updating the standard voltage, in correspondence with standard voltage data, which indicate a value of the set or updated standard voltage; an estimating device for estimating a value of the bias voltage of the angular velocity sensor at each time between times of setting or updating the standard voltage, as a function of time, on the basis of a plurality of the stored standard voltage data and a plurality of the stored time data; and a correcting device for correcting the angular velocity calculated by the calculating device on the basis of a difference between a value of the standard voltage used in the calculating device and the estimated value of the bias voltage.
According to the apparatus for detecting an angular velocity of the present invention, the bias voltage, which is the output voltage outputted from the angular velocity sensor, is firstly set as the standard voltage when a predetermined condition is satisfied. Then, after an operation of the apparatus for detecting an angular velocity is started, every time when the predetermined condition is satisfied, the standard voltage is updated by the setting device. Then, the angular velocity is calculated by the calculating device, on the basis of the output voltage with using the set or updated standard voltage as a standard. On the other hand, the time data, which indicate a time of setting or updating the standard voltage, is stored into a memory or the like of the storing device, in correspondence with the standard voltage data, which indicate a value of the set or updated standard voltage, every time when the standard voltage is set or updated. Then, the value of the bias voltage of the angular velocity sensor at each time between times of setting or updating the standard voltage is estimated by the estimating device, as a function of time. This estimation is performed, under a condition that at least two time data and two standard voltage data corresponding to the time data are stored, on the basis of these standard voltage data and time data. Then, the angular velocity calculated by the calculating device in the past is corrected by the correcting device, on the basis of the difference between the value of the standard voltage used in the calculating device and the above-mentioned estimated value of the bias voltage.
Therefore, within a period while the bias voltage can not be measured, the calculated angular velocity includes errors caused by a change by the start drift, the temperature drift of the bias voltage or the like. However, when the standard voltage is updated next time, i.e., when the bias voltage can be measured next time, the errors caused by the change of the bias voltage can be corrected backward into the past.
Incidentally, the bias voltage value not only in the past but also in the future may be estimated by the estimating device, from the latest time of updating and may be used as the standard voltage in calculating the angular velocity before the correction.
In one aspect of the apparatus for detecting an angular velocity, the apparatus is further provided with a judging device for judging whether or not the predetermined condition is satisfied, wherein the setting device sets or updates the standard voltage depending on a judgment result in the judging device.
According to this aspect, it is judged by the judging device whether or not the predetermined condition is satisfied. Then, the standard voltage is set or updated by the setting device, depending on this judgment result in the judging device. Therefore, because the standard voltage can be certainly set or updated when the bias voltage can be newly measured, it is possible to set the standard voltage with a high accuracy.
In another aspect of the apparatus for detecting an angular velocity, the estimating device uses an n function (n is a natural number), which approximates a change of the bias voltage value with respect to time, as the function.
According to this aspect, the process of estimating uses an n function or n-dimensional function. For example, an n function in this kind is obtained by solving simultaneous equations made by n standard voltages in the past and the corresponding time. Moreover, it is possible to estimate a change of the bias voltage value from more standard voltage values by using the least square method for more standard voltage values in the past.
The above object of the present invention can be achieved by an apparatus for detecting an angle provided with: a setting device for setting a bias voltage, as a standard voltage, which is an output voltage outputted from an angular velocity sensor mounted on a movable thing in response to an angular velocity when a predetermined condition is satisfied as well as updating the standard voltage every time the predetermined condition is satisfied; a calculating device for calculating the angle of the movable thing on the basis of a difference between the output voltage and the set or updated standard voltage; a storing device for storing time data, which indicate a time of setting or updating the standard voltage, in correspondence with standard voltage data, which indicate a value of the set or updated standard voltage; an estimating device for estimating a value of the bias voltage of the angular velocity sensor at each time between times of setting or updating the standard voltage, as a function of time, on the basis of a plurality of the stored standard voltage data and a plurality of the stored time data; and a correcting device for correcting the angle calculated by the calculating device on the basis of a difference between a value of the standard voltage used in the calculating device and the estimated value of the bias voltage.
According to the apparatus for detecting an angle of the present invention, the bias voltage, which is the output voltage outputted from the angular velocity sensor, is firstly set as the standard voltage when a predetermined condition is satisfied. Then, after an operation of the apparatus for detecting an angle is started, every time when the predetermined condition is satisfied, the standard voltage is updated by the setting device. Then, the angle of the movable thing (e.g., the travel angle or azimuth of the vehicle) is calculated by the calculating device, on the basis of the difference between the output voltage and the set or updated standard voltage. On the other hand, the time data, which indicate a time of setting or updating the standard voltage, is stored into a memory or the like of the storing device, in correspondence to the standard voltage data, which indicate a value of the set or updated standard voltage, every time when the standard voltage is set or updated. Then, the value of the bias voltage of the angular velocity sensor at each time between times of setting or updating the standard voltage is estimated by the estimating device, as a function of time. Here, this estimation is performed, under a condition that at least two time data and two standard voltage data corresponding to the time data are stored, on the basis of these standard voltage data and time data. Then, the angle calculated by the calculating device in the past is corrected by the correcting device, on the basis of the difference between the value of the standard voltage used in the calculating device and the above-mentioned estimated value of the bias voltage.
Therefore, within a period while the bias voltage can not be measured, the calculated angle includes errors caused by a change by the start drift, the temperature drift of the bias voltage or the like. However, when the standard voltage is updated next time, i.e., when the bias voltage can be measured next time, the errors caused by the change of the bias voltage can be corrected backward into the past.
Incidentally, the bias voltage value not only in the past but also in the future may be estimated by the estimating device, from the latest time of updating and may be used as the standard voltage in calculating the angle before the correction.
In one aspect of the apparatus for detecting an angle, the apparatus is further provided with a judging device for judging whether or not the predetermined condition is satisfied, wherein the setting device sets or updates the standard voltage depending on a judgment result in the judging device.
According to this aspect, it is judged by the judging device whether or not the predetermined condition is satisfied. Then, the standard voltage is set or updated by the setting device, depending on this judgment result in the judging device. Therefore, because the standard voltage can be certainly set or updated when the bias voltage can be newly measured, it is possible to set the standard voltage with a high accuracy.
In another aspect of the apparatus for detecting an angle, the estimating device uses an n function (n is a natural number), which approximates a change of the bias voltage value with respect to time, as the function.
According to this aspect, the process of estimating uses an n function or the like. For example, an n function in this kind is obtained by solving simultaneous equations made by n standard voltages in the past and the corresponding times. Moreover, it is possible to estimate a change of the bias voltage value from more standard voltage values by using the least square method for n+2 or more standard voltage values in the past.
In another aspect of the apparatus for detecting an angle, the calculating device converts a value, which is obtained by integrating on a time axis a difference between the output voltage and the set or updated standard voltage to a turning angle of the movable thing, and the correcting device corrects the angle by correcting the turning angle in response to a value, which is obtained by integrating on a time axis a difference between the value of the standard voltage used in the calculating device and the estimated value of the bias voltage.
According to this aspect, it is possible to calculate the turning angle of the movable thing relatively easily by the difference between the output voltage of the angular velocity sensor and the standard voltage by use of an integrating circuit. Further, it is possible to calculate a correction amount to the turning angle relatively easily by the difference between the standard voltage value used in the calculating device and the estimated value of the bias voltage by use of the integrating circuit. Therefore, it is possible to correct the angle on the basis of the corrected turning angle.
Incidentally, the angular velocity sensor of the present invention described above, is a gyro sensor such as a vibration gyro, a gas rate gyro, an optical fiber gyro, or the like. The angular velocity sensor may be one except the gyro sensor, for example, one of such an arbitrary type that magnitude of the output voltage based on the bias voltage corresponds to the angular velocity. When the angular velocity sensor in which the bias voltage changes more or less with time by the temperature drift, the start drift, or the like, the method of and the apparatus for detecting an angular velocity and the method of and the apparatus for detecting an angle of the present invention are effective.
The above object of the present invention can be achieved by a navigation system provided with: the above-mentioned apparatus for detecting an angle of the present invention (including its various aspects); the angular velocity sensor; and a displaying device for displaying the corrected angle in a predetermined format.
According to the navigation system of the present invention, because it is provided with the above-mentioned apparatus for detecting an angle, even if the bias voltage of the angular velocity sensor changes by the temperature drift or the like, the angle can be detected with a high accuracy. Therefore, the displaying device can display a highly accurate angle (e.g., a drive azimuth of a vehicle).
The above object of the present invention can be also achieved by a program storage device readable by a computer. The program storage device stores a program of instructions to cause the computer to function as at least one portion of the above-described apparatus for detecting an angle of the present invention (including its various aspects).
According to the program storage device, such as a CD-ROM (Compact Disc-Read Only Memory), a ROM, a DVD (DVD Read Only Memory), a floppy disk or the like, of the present invention, the above described apparatus for detecting an angle of the present invention can be relatively easily realized as a computer reads and executes the program of instructions or as it executes the program after downloading the program through communication device. Moreover, the program of instructions can be sent from a central device with an application program required for the navigation or other data such as a map.
The above object of the present invention can be also achieved by another program storage device readable by a computer. The program storage device stores a program of instructions to cause the computer to function as at least one portion of the above-described apparatus for detecting an angular velocity of the present invention (including its various aspects).
According to the program storage device, such as a CD-ROM, a ROM, a DVD, a floppy disk or the like, of the present invention, the above described apparatus for detecting an angular velocity of the present invention can be relatively easily realized as a computer reads and executes the program of instructions or as it executes the program after downloading the program through communication device. Moreover, the program of instructions can be sent from a central device with an application program required for the navigation or other data such as a map.
The above object of the present invention can be also achieved by a computer data signal embodied in a carrier wave and representing a series of instructions for a computer. The series of instructions causes the computer to function as at least one portion of the above-described apparatus for detecting an angle of the present invention (including its various aspects).
According to this computer data signal embodied in the carrier wave of the present invention, as the computer downloads the program in the computer data signal through a computer network or the like, and executes this program, it is possible to realize the above described apparatus for detecting an angle of the present invention.
The above object of the present invention can be also achieved by another computer data signal embodied in a carrier wave and representing a series of instructions for a computer. The series of instructions causes the computer to function as at least one portion of the above-described apparatus for detecting an angular velocity of the present invention (including its various aspects).
According to this computer data signal embodied in the carrier wave of the present invention, as the computer downloads the program in the computer data signal through a computer network or the like, and executes this program, it is possible to realize the above described apparatus for detecting an angular velocity of the present invention.
The nature, utility, and further features of this invention will be more clearly apparent from the following detailed description with reference to preferred embodiments of the invention when read in conjunction with the accompanying drawings briefly described below.